1. Field of the Invention
The present invention relates to a hexagonal type barium titanate powder, a producing method thereof and a dielectric composition including the hexagonal type barium titanate as a main component, more precisely, relates to a dielectric ceramic composition which is preferable to produce a dielectric layer of electronic components used for temperature compensation. Also, the present invention relates to an electronic component having a dielectric layer composed of the dielectric ceramic composition.
2. Description of the Related Art
Among ceramic capacitors as an example of electronic components, some is used for temperature compensation purpose. For capacitors used for such purpose, it is required that change of characteristics such as specific permittivity and the like in a wide temperature range is small.
As for dielectric material of such capacitors, for example, a material based on paraelectrics such as (Ca) (Ti, Zr)O3 is used (refer to Japanese Patent No. 4325900). However, because based on the paraelectrics, a comparatively high specific permittivity cannot be obtained. For example, when using dielectric material disclosed in Japanese Patent No. 4325900, specific permittivities resulted in 50 or less. Therefore, there is a limitation of increasing a capacitor capacity.
In the meantime, as for a new material having comparatively high specific permittivity, for example, hexagonal barium titanate can be exemplified. Although the hexagonal barium titanate has lower specific permittivity than the barium titanate having perovskite type crystal structure (tetragonal, cubic), it shows higher permittivity than the paraelectrics.
However, in a crystal structure of the barium titanate, hexagonal structure is a metastable phase, normally, it can be exist only at 1460° C. or higher. Therefore, in order to obtain the hexagonal barium titanate at room temperature, it is necessary to cool rapidly from the high temperature of 1460° C. or higher.
In this case, a specific surface area of the obtained hexagonal barium titanate becomes 1 m2/g or less because of the rapid cooling from the high temperature, thus a coarse powder is only obtained. When producing electronic components with thinner dielectric layer by using such coarse powder, there is a problem that it cannot maintain the sufficient reliability, because the powder fails to adapt to the thinner dielectric layer.
By the way, as for a producing method of the hexagonal bariumtitanate, for example, Non-Patent Literature 1 discloses that BaCO3, TiO2 and Mn3O4 are used as starting raw materials and are heat-treated. By this means, a transformation temperature to hexagonal phase can be lowered, hexagonal barium titanate in which Mn is solid-soluted is obtained by a heat treatment at a temperature lower than 1460° C.
However, specific surface area of the hexagonal barium titanate obtained in the Non-Patent Document 1 is approximately 1.6 m2/g, thus it is insufficient for applying a thinner dielectric layer in the electronic components even though using this hexagonal barium titanate powder.
Non-Patent Literature 1 is “Properties of Hexagonal Ba(Ti1-xMnx)O3 Ceramics: Effects of Sintering Temperature and Mn Content”, Japanese Journal of Applied Physics, 2007 Vol. 46 No. 5A 2978-2983.